There are known a very large number of different switching means for electric kettles of the above kind, for example, there are "steam actuated switching means" to switch the kettle off when it boils, "dry overload switching means" to switch the kettle off if the immersion heater overheats, and manually operable "on/off switching means".
There are sold a very large number of electric kettles which have only a dry overload switching means, because they are relatively inexpensive and because the dry overload switching means are usually small enough to be inserted between the metal head and a molded plastics plug socket for an electrically supply cable connector, thereby to avoid having a large switch housing projecting from the kettle body. This type of kettle is known as a "non-automatic" kettle, and has the advantages of low manufacturing cost, simple manufacture, easy repair and durability; and only occasionally are there any warranty (guarantee) claims due usually to overheating.
There are also sold very large numbers of electric kettles of the type known as "automatic" kettles, which include steam actuated switching means, and usually also dry overload switching means. The steam actuated switching means normally controls the kettle so that the dry overload switching means becomes of secondary importance. In most automatic kettles there is a small vent near the top of the kettle body to allow steam to flow to the steam actuated switching means, and therefore there is a need to provide means for excluding steam and water condensate from the electrical contacts and electrical conductors of the switching means, thus making automatic kettles complicated and expensive to manufacture.
In order to reduce the cost of such automatic kettles it is known to use an on/off switching means which is manually operable to close or to open and close a single set of electrical switch contacts, and to mechanically (but not electrically) interconnect the mechanism of on/off switching means with a dry overload responsive actuating mechanism and a steam responsive actuating mechanism. This reduces the number of electrical components but gives rise to problems because steam and water can follow the mechanical interconnections of the actuating mechanisms to the electrical switch contacts, and the mechanical interconnections are difficult to adjust during manufacture and are prone to malfunctions in use, causing the kettle to switch off before it has boiled or not to switch off when it does boil, giving rise to expensive warranty claims.
Other automatic kettles have employed the more expensive alternative of using separate sets of electrical switch contacts in separate dry overload and steam actuated switching means, each set of contacts being individually protected from steam and condensate. However, these kettles are very expensive, difficult to repair and can suffer from electrical problems due to the large number of electrical contacts and connections, with resultant warranty costs.
A great amount of research and development has been devoted to reducing the cost of the component parts of the switching means for automatic kettles, and there are available to kettle manufacturers switch assemblies which are mass produced by switch manufacturers. Some of these switch assemblies incorporate both dry overload and steam actuated switching means. However, the kettle manufacturer has no way of fully testing such bought out switch assemblies until they have been incorporated into the kettles, so that any switch faults result in complete kettles having to be scrapped, or dismantled for salvage at very considerable cost to the kettle manufacturer. Furthermore, materials and manufacturing tolerances can give rise to incompatibility between some batches of switch assemblies and some batches of immersion heaters, and often this incompatibility can not be detected by the kettle manufacturer until after these parts have been incorporated into the kettle making them faulty. The resultant expense to the kettle manufacturer is large if the faulty kettles are detected by the kettle manufacturer, but can be very great if the faults in the kettles only become apparent after a period of use by customers. Thus these switch assemblies can result in an overall increase in costs, while not overcoming the previously discussed switching and other problems with automatic kettles.
There is a further problem with automatic kettles, in that if they are overfilled with water or tilted when full, water can flood out of the steam vent at a rate sufficient to flood the switching means, and hitherto the best answer to this problem has been to place the steam actuated switching means in the handle well above the water level, but this answer is expensive and requires lengthy electrical connections to the immersion heater.